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Aging Matters

In the news this week was a huge British study in The Lancet about longevity trends worldwide. The headlines were about the admirable progress that our world is making toward fewer avoidable deaths in the underdeveloped world. Life expectancy there is going up, for reasons that have nothing to do with aging. The secondary headline: Life expectancy in the US is falling further behind other rich countries, and this is much more true of American women than American men. This is a national humiliation, and it has everything to do with economics.

Good news for the underdeveloped world

From 1970 to 2010, life expectancy the world over increased from 59 to 70. Threescore and ten is no longer the province of the rich, but an expectation for our great human family. Deaths of children younger than 5 years declined in absolute terms by almost 60% since 1970, despite a doubling in world population.

In the developed countries, it isabout aging.

In 1970, in the developed world, the low-hanging fruit had already been picked clean: infectious disease, childbirth, and infant mortality were no longer major factors in actuarial risk. Most people could expect to live out their full life span of about 70 years. Everyone expected – that is, demographers, epidemiologists and policy-makers – everyone expected that the life expectancy had risen to a natural limit, and that any further progress would be slow and difficult. But surprise! Since 1970, countries with the longest life expectancies have continued to improve just as fast as before, even though the progress is now all “at the back end”. Increase in life expectancy since 1970 has been more than 10 years in Japan, 9 years in Europe. For every year that goes by, 3 months are added to life expectancy. And this progress applies almost entirely to people over 70. Seniors today are living longer because they are healthier. They are more engaged and active than their parents’ generation.

Compare a picture of a 60-year-old in 1912 to a 70-year-old today. James Vaupel is the world’s most famous, if controversial, demographer. (He is not among the authors of the Lancet study.) By his definition, we have succeeded in delaying the aging process by a decade.

The evidence suggests that deterioration, instead of being stretched out, is being postponed: levels of mortality and other indices of health that used to prevail at age 70 now prevail at age 80, and levels that used to prevail at age 80 now prevail at age 90.

Exactly “how” is a mystery, but there is wide agreement that it has been a composite of many factors. “It seems that death is being delayed because people are reaching old age in better health.”

Bad news for US Women

In 1970, both Europe and Japan had recently slipped by the US as leaders in life expectancy. The trend has continued for 40 years, and women in Japan now live 5½ years longer than American women. For men the gap is 3 years. European women and men are halfway between their counterparts in the US and Japan.

(These numbers come from the life expectancy table by country that is the primary result of the Lancet study.)

Life expectancy in the US is increasing much more slowly than in other parts of the world, and for women, it’s hardly improving at all. The New York Times reports

But while developing countries made big strides the United States stagnated. American women registered the smallest gains in life expectancy of all high-income countries’ female populations between 1990 and 2010. American women gained just under two years of life, compared with women in Cyprus, who lived 2.3 years longer and Canadian women who gained 2.4 years. The slow increase caused American women to fall to 36th place in the report’s global ranking of life expectancy, down from 22nd in 1990. Life expectancy for American women was 80.5 in 2010, up from 78.6 in 1990.

A lot of the reason for the difference comes from economics. There is a much wider gap in the US than anywhere else in the developed world in access to health care, and this shows up as a major gap in life expectancy between rich and poor. Life expectancy for the working class in America lags the rich by 5 years.

But lest rich Americans should feel complacent about this situation, the Japanese have pulled ahead of the US by more than 6 years. That means that the average Japanese is living longer than the richest Americans.

Footnote: What do life expectancy tables mean?

This is a much more interesting and complicated question than it ought to be. The issue is that the world is changing so fast, and any “snapshot” of mortality rates at different ages reflects people who were born at different times. Life expectancy numbers as quoted are not the life expectancy of an infant born today, or for any particular person or set of people. That’s because the numbers are calculated using a composite of all the people dying today. So the standard tables are based on infant mortality of babies just born, combined with war statistics, suicides and traffic accidents for young men born in the 1980s and geriatric statistics for people born in the 1920s.

Based on Vaupel’s claim that 1 year of life is being added for every four years that passes, we might make a very crude correction to tables of life expectancy by tacking on an extra 1/3. If the life table says you have 30 years left to live, you can interpret that to mean 40. (Why is it 1/3 rather than ¼? The answer is purely mathematical, and derives from the fact that while you’re living out your ¼, the world is advancing and giving you another ¼ of ¼, and then while you’re living out that period…etc.)

So what is the life expectancy of a child born today? That’s a question that is as difficult to forecast as anything else about the coming century – war and peace, global warming, the Apocalypse or the Singularity. Based purely on demographic trends and not biomedical forecasts, Vaupel says “The future is uncertain, but it seems plausible that very long lives may be the probable destiny of younger people alive today.”

Richard Karpinski writes:
One possible mechanism for achieving longer healthy life is that by introducing new immune system challenges, one builds her immune system while responding to them. Living with a child who picks up infections from other children exposes one to infectious agents that childless families do not encounter.

I hope that we can now continue to extend the breadth, depth, and length of individual health histories available for scientific study so as to make a sound basis for specific recommendations for what to ingest and how to exercise. Facts seem often useful.

Mitteldorf responds:
Yes – isn’t it curious that challenging our bodies with pathogens leads to longer life?
There’s also another mechanism that might help explain the mechanism by which parenthood contributes to longevity: When a woman is pregnant, some of the foetus’s stem cells migrate into the mother’s body, and become functioning parts of her metabolism, including her immune system.